The thing that charges our batteries on the engine

[Nous Defions]

Check out Beachbummer's post above. That's what we are talking about. Also the terminal fuse instruction is clear that it should not be installed on the battery post. It will be connected to the battery switch as pointed out by Blue Sea rep. See photos above.

 

[212s]

I have read some where that: Each engine on the 240 has a rectifier regulator that limits maximum output voltage to 13 volts between 2000-3500 rpm's, with a stator coil output voltage of 8.3v cranking, 36.4v@2000rpm, and 64.7v@3500rpm.

Another site says there are 40 amp magnetos on each engine.

If it's correct that each engine has a 40 Amp charging system does that mean the total amps possible for a charge is 80 amps?

Any electrical guru's out there that can clarify volts vs. amps vs total?

I believe the magnetos can produce about 30amps or more at 3500rpm, and the rectifiers are rated at 28amps - that's from the basic info I've been able to find and the numbers on the rectifiers. But don't take that as fact. Given the battery cables are 4awg they can carry about 85amps, so fuse for that amount to protect the wires from overheating.

Now when it comes to charging, you have to take into account what kind of batteries you have. Sealed Lead Acid (SLA) can be charged at about C/5 so for a typical G24 100ah battery, you can expect about 20amps for a good charge rate that's not too fast causing heat and gassing. I'm guessing the ACR in the battery switch limits current to the batteries as 56amps would be too fast even with dual batteries, as the ACR charges the start battery first then switches to the house. I haven't checked the full wiring yet, but from visual inspection of charging and voltages, I have a feeling one motor charges and the other supplies current for the house and motor electrical.
Need to get my hands on a service manual...or poke around some more in the wiring.

 

[marcham]

Reading Blue Sea Wire & Fuse Size Chart, I should be using a 100-125A fuse if I read the chart right. Charging Amps:80, Wire Size:4.
What I don't want is to be tooling along and blowing fuses because I went too small nor tooling along and having a melt down because I went to big.
Do I trust the instructions and call it a day or am I over thinking this?

100 or 125A, doesn't really matter. I wouldn't bother carrying a spare. If one blows, you have an electrical problem / short you have to repair. You can always manually set the switch to both to charge both batteries. Your batteries will never draw 80A unless they are lithhium. The acr doesn't selectively charge the batteries, it combines them in parallel when the regulator voltage is above a pre set number. They will normally combine both for the entire time the engine is running.